can we use your allowance money? >> no! mom! >> the only problem i can see with this is that i think i'd be tempted to spend a lot of my money buying seeds and plants. and i don't think my husband would be very happy. >> i can see that. >> reporter: in fact, 15% of those 80 million farmville players do spend real money on the game. 5% spend at least $20 a month. that pay-to-play option, along with advertising revenue, has helped build a very profitable business for farmville's parent company zenya, which is expected to make $450 million this year alone. farmville outsiders don't understand the fuss. >> i don't understand why you want to build a farm. on facebook. i just don't. >> some of your friends play farmville? >> yes, it's stupid. >> my brother is a junior in high school, he loved it, his friends were the first ones to tell me about it. now my parents will be, like, telling me about their friends who are trying to get them to play farmville. >> reporter: compulsion or hobby, maria isn't quite sure. >> i would just say that